NEW YORK -- General Electric has agreed to buy Texas-based oilfield equipment maker Lufkin Industries for $3.1 billion, furthering an effort by GE to grow its oil and gas operations.GE said Monday that it would pay Lufkin shareholders $88.50 per share, a 38 percent premium over Lufkin's closing price on Friday of $63.93. Lufkin's shares (ticker: LUFK) jumped 37.6 percent Monday to $87.96.The companies valued the deal at $3.3 billion, which includes $200 million in debt to be assumed by GE.Lufkin, based in the East Texas city of the same name northeast of Houston, is best known for its familiar "rocking horse" pump jacks seen in oil fields. (They are not used on natural gas wells such as those in North Texas' Barnett Shale.)The pumps pull oil from deep in the well when there's not enough natural pressure to force the liquid to the surface. Daniel Heintzelman, chief executive of GE's oil and gas unit, said 94 percent of oil wells will require some form of pumping, known in the industry as artificial lift.Lufkin has 4,500 employees in more than 40 countries. It also makes submersible pumps, power transmission equipment and well automation systems.CEO Jeff Immelt is in the process of transforming GE from a sprawling conglomerate to one that is more tightly focused on providing services and equipment to industrial customers. The company has shed divisions such as NBC Universal and is shrinking its banking operations.Immelt indicated that the company would use some of its enormous cash balance to buy midsized companies that fit well into what the company already does. GE makes aircraft engines, natural gas-fired turbines and generators, wind turbines, medical devices and locomotives.In Tarrant County, GE's transportation unit also has manufacturing facilities making locomotives and large mining vehicles.GE is putting particular focus on oil and gas, hoping to capitalize on the boom in extracting oil from difficult places, such as deep offshore, shale formations under several U.S. states, or older depleting oil fields. GE bought Wellstream, a maker of flexible pipes for gathering oil undersea, in 2010, and a division of the John Wood Group, a maker of pumps and control systems, in 2011."Wells in the future are going to be more and more technically challenging," said Heintzelman.GE's oil-and-gas-related revenue has tripled since 2005, to $15 billion, accounting for 10 percent of the company's $147 billion total revenue last year.Christopher Glynn, an analyst at Oppenheimer, said the deal fits nicely into GE's strategy. He said that as oil and gas continue to get more expensive to produce, there will be ample opportunity for GE's growing oil and gas division to offer products and services to help keep those costs in check and make fields more productive.